The expression “plasticizer” is used in the technical chemical literature for substances capable, simple by virtue of their admixture, of converting a hard, brittle substance into a soft, extensible, tough or elastic preparation. The expression is used in very many different contexts. By way of example, it is often used in concrete processing (see for example WO 98 58 887 A1) and in rocket fuel production (see for example U.S. Pat. No. 3,617,400). The expression “plasticizer” is used in the narrower sense to mean materials added during polymer processing which can alter the mechanical properties of thermoplastic polymers in the abovementioned manner. Examples of polymers processed with plasticizers are polyvinyl chloride, polyvinyl butyral, polyamide and cellulose acetate. The largest quantitative use is in polyvinyl chloride.
The suitability of a substance as plasticizer for a particular polymer depends on the properties of the polymer. In the last 50 years, increasingly stringent technical and economic requirements placed upon production processes and on plasticized plastics have meant that the substances preferred as plasticizer differ as a function of the polymer. Substances having good suitability as plasticizer in a particular polymer here typically have low suitability or indeed no suitability in another polymer.
Triacetin (glycerol triacetate, Chemical Abstracts Registry Number 102-76-1) is described as plasticizer for cellulose acetate (see for example GB 317,443), starch (see for example WO 9005161 A1) and polylactide (see for example U.S. Pat. No. 6,117,928). However, triacetin is not known for use as plasticizer in polyvinyl chloride. The comparative examples presented below demonstrate that the solution temperature of triacetin in polyvinyl chloride is above 200° C. This confirms that triacetin has extremely poor compatibility with polyvinyl chloride.
In the context of plasticizers, the solution temperature is the temperature at which gelling produces a homogeneous phase from a polyvinyl chloride suspension in a plasticizer. A low solution temperature indicates that the plasticizer has good gelling power. This is often desirable, since it is then possible to process the material at low temperatures, saving energy. Substances with solution temperatures above 180° C. are unsuitable as plasticizers for polyvinyl chloride (L. Meier: “Weichmacher” [Plasticizers], in R. Gächter, H. Müller (Ed.): Taschenbuch der Kunststoffadditive [Plastics additives handbook], 3rd Edition, pp. 361-362, Hanser Verlag, Munich 1990).
When polyvinyl chloride is processed with plasticizers, there are other properties of the plasticizer that can play a decisive role, alongside a sufficiently low solution temperature. By way of example, an important factor in the production of polyvinyl chloride plastisols can be that the viscosity of the polyvinyl chloride suspension initially prepared in the plasticizer is low, enabling it to be processed easily. In many applications, the intention is that the subsequent gelling of the suspension on exposure to heat should proceed at maximum rate, in order to limit the amount of time and energy required. An example of a plasticizer used in such instances in the prior art is benzyl butyl phthalate.
The intended function of the plasticizer in the fully gelled, plasticized polyvinyl chloride preparation is not only to provide the desired softness but also by way of example to have maximum resistance to migration into adjacent media.
Further demands placed upon plasticizers result from the desire to avoid hazards to humans and the environment. By way of example, under European Union Directive 2005/84/EC it is no longer permissible to use the plasticizers di(2-ethylhexyl)phthalate, dibutyl phthalate and benzyl butyl phthalate in toys or baby items, or to use the plasticizers diisononyl phthalate, diisodecyl phthalate and di-n-octyl phthalate in toys or baby items which might enter children's mouths. There is therefore a particular requirement for suitable replacement materials for the abovementioned plasticizers di(2-ethylhexyl) phthalate, dibutyl phthalate and benzyl butyl phthalate.
In view of these restrictions, which to many consumers can appear to be confusing and worrying, many producers are actually adopting a generalized approach of avoiding all phthalate-containing plasticizers in the production of plasticized polyvinyl chloride. The result of this is a requirement for phthalate-free plasticizers which in terms of processability and service properties achieve the performance level of phthalate-containing plasticizers.
In relation to the abovementioned fast gelling, there is a requirement for a replacement material for benzyl butyl phthalate, in particular a requirement for a phthalate-free replacement material for benzyl butyl phthalate, or for a replacement material which is better than previous phthalate-free plasticizers in PVC but whose performance level is comparable with that of phthalate-containing plasticizers.
It was an object of the present invention to provide a plasticizer with low solution temperature and short gel time which is a suitable replacement material for di(2-ethylhexyl) phthalate, and for dibutyl phthalate, and in particular for benzyl butyl phthalate. The preparations according to the invention achieve this object.